The present invention relates to an exhaust energy recovery system for a combustion engine that recovers and recycles the energy of exhaust gas (exhaust energy).
Japanese Laid-Open Patent Publication No. 3-54313 discloses such exhaust energy recovery system for a combustion engine. The recovery system includes a vane type displacement expansion device in an exhaust passage of the combustion engine. The output shaft of the expansion device is mechanically coupled to and driven by a crankshaft of the engine. The output shaft of the expansion device is rotated by the exhaust energy, and the rotation of the output shaft is transmitted to the crankshaft. Thus, the exhaust energy is recovered to assist the engine output.
However, in the above exhaust energy recovery system, the output shaft of the displacement expansion device and the crankshaft are mechanically coupled to each other. Therefore, the rotational speed of the displacement expansion device is determined in accordance with the rotational speed of the engine regardless of the flow rate of exhaust gas introduced into the displacement expansion device. Therefore, depending on the driving condition of the engine, the exhaust energy is not sufficiently recovered. Further, the system can cause the load of the engine to increase or the back pressure to increase.
Furthermore, since the exhaust energy is recovered by mechanical means, the recovered exhaust energy is only used for assisting the engine output. This extremely limits the flexibility of the recycling of the recovered exhaust energy.